FIG. 11 is a perspective view illustrating a conventional high frequency IC package. In the figure, a package body 1 comprises a dielectric part 1a comprising ceramic or the like and a chip bonding part 1b comprising metal or the like. A signal transmission line 6 is disposed on the dielectric part 1a. The chip bonding part 1b is grounded. High frequency IC chips 2a and 2b are disposed on the chip bonding part 1b. Each of the IC chips includes input-output pads 3 through which the IC chip is connected to the adjacent IC chip or to the signal transmission line 6 of the package 1.
The IC chips 2a and 2b are fixed on the chip bonding part 1b using solder, conductive resin, or the like. Thereafter, as shown in FIG. 12, a metal wire 4 comprising Au, Al, or the like is pressed on the pad 3 of the IC chip 2 using a wedge type blade 5 of a bonding apparatus (not shown) and adhered to the pad 3 by thermocompression bonding or ultrasonic bonding.
FIG. 13 is a perspective view illustrating the package 1 after the wire-bonding process. In FIG. 13, a metal wire 4b connects the pads 3 of the adjacent IC chips 2a and 2b to each other and a metal wire 4a connects the pad 3 of the IC chip 2a to the signal transmission line 6 of the package 1. The length of each metal wire is about 300 microns. In this structure, high frequency signals are transferred through the IC chips and the signal transmission line via the metal wires.
The metal wire for connecting the high frequency IC chips has the following drawbacks. Since the characteristic impedance of the metal wire significantly varies according to its length and shape, a large signal reflection occurs at the boundary between the metal wire and the bonding pad of the IC chip. In addition, the large inductance of the metal wire increases the signal attenuation. For example, when an Au wire having a length of 1 mm and a diameter of 25 microns is employed, the attenuation increases with the increase in the frequency as shown in FIG. 14, adversely affecting the device characteristics. When the frequency exceeds 26 GHz, the attenuation exceeds 10 dB (power ratio of 1/10 or below), which makes the practical use of the device difficult.
Meanwhile, Japanese Published Patent Application No. 3-120736 discloses a semiconductor device in which a high frequency IC chip is connected to a coplanar transmission line on a package via bump electrodes. This structure is illustrated in FIGS. 15(a) and 15(c). In these figures, the coplanar transmission line comprising a signal conductor 31 and grounding conductors 32 is disposed on a ceramic substrate 33. The ceramic substrate 33 is disposed on a metal module frame 30. Bump electrodes 34 are disposed on the conductors 31 and 32. When mounting the high frequency IC chip 2 on the substrate, the input-output pads 3 of the IC chip 2 are pressed onto the bump electrodes 34 while applying heat, whereby the pads 3 are electrically and physically connected to the bump electrodes 34.
FIG. 16 is a perspective view, partly broken away, illustrating an impedance-matched film carrier described in "20 GHz Band MMIC Modules Assembled by Impedance-Matched Film Carrier" at page 29 of 1989 Autumn National Convention Record, The Institute of Electronics, Information and Communication Engineers. In FIG. 16, grounding conductors 41 are disposed on the rear surface of a polyimide film 40, and a signal conductor 42 is disposed between the grounding conductors 41, providing a coplanar transmission line. Portions of the polyimide film 40 are opened to expose the coplanar transmission line. When mounting a high frequency IC chip on the film carrier, input-output pads of the IC chip (not shown) are connected to the coplanar transmission line via the openings 43.
In the above-described prior arts, however, it is necessary to form the coplanar transmission line on the package or the film carrier in advance and in accordance with the shape or the arrangement pattern of the high frequency IC chip to be connected thereto, resulting in an increased production cost and a restricted pattern layout of the IC chip.